IDG News Service (London Bureau) — The next time you splurge on a double latte and sip it while browsing the Internet via the café's Wi-Fi, beware of the "evil twin."

That's the term for a Wi-Fi access point that appears to be a legitimate one offered on the premises, but actually has been set up by a hacker to eavesdrop on wireless communications among Internet surfers. Unfortunately, experts say there is little consumers can do to protect themselves, but enterprises may be in better shape.

With the growth in wireless networks, the "evil twin" type of attack is on the rise, said Phil Cracknell, president of the U.K. branch of the Information Systems Security Association. Such attacks are much easier than others seeking log-ins or passwords, such as phishing, which involves setting up a fraudulent website and luring people there, Cracknell said.

A rogue Wi-Fi connection can be set up on a laptop with a bit of simple programming and a special USB thumb drive that acts as an access point. The access points are hard to trace, since they can suddenly be shut off, and are easy to build, Cracknell said.

The growth in the number of Wi-Fi networks poses increasing opportunities for hackers, who can make their networks appear to be legitimate by simply giving their access point a similar name to the Wi-Fi network on the premises. Since the hacker may be physically closer to the victim than the real access point, their signal will be stronger, potentially drawing more victims.

The hacker's computer can be configured to pass the person through to the legitimate access point while monitoring the traffic of the victim. Several free programs available on the Internet can decode packets to reveal clear-text log-ins and passwords.

"You are going to harvest some incredible information in a short span of time with a rogue hotspot," Cracknell said.

Corporate users can protect themselves by using VPN when logging into company servers, Cracknell said. But consumers are at a particular disadvantage, since they are likely not using VPN and will access free Web e-mail applications that could send passwords in clear text.

Wi-Fi hotspot owners tend to be "absolutely ignorant" of the attack, although they should regularly monitor their network for rogue access points, Cracknell said. Another problem is reporting: Victims may not even know how their information was pinched, and those who run the hotspot may be reluctant to reveal that hackers exploited their network.

Consumers can protect themselves at least one way: Be wary of free hotspots. Many airports and cafés charge for access, so a free hotspot could be designed to ensnare potential victims. Also, the attack has been used in hotels, with the "evil twin" actually coming from a nearby hacker guest.

The risk is still great. "This [attack] is foolproof to a degree," Cracknell said.